1. Field of the Invention
The present invention relates to diffusion bonding and, more particularly, to a fixture and method for holding workpiece surfaces in contact under controlled pressure during bonding.
2. Description of the Prior Art
Diffusion bonding, including TLP.RTM. bonding, is a well known technique for joining metal or alloy parts together, examples of various processes being found in U.S. Pat. Nos. 3,530,568; 3,678,570; 3,680,197; 3,713,207 and others. Generally, such bonding processes require elevated temperatures and pressures for attainment of satisfactory bonding. In the past, however, there has been a problem in bringing the workpiece surfaces together under sufficient pressure to effect bonding without, at the same time, distorting the surfaces and/or the fixture holding the workpieces together. Some prior art workers have utilized dead weight loading which, although capable of applying controlled pressure, requires a plurality of bulky weights, large furnaces to accommodate them and massive equipment capable of handling the heavy loads. Other prior art workers, such as represented by U.S. Pat. No. 3,762,032, have utilized fixtures having components of different thermal expansion characteristics to generate bonding pressure. However, these fixtures have been found to be disadvantageous in that bonding pressure is not readily controllable, resulting in frequent workpiece and fixture distortion from excessive pressure. This distortion problem is especially severe and costly when workpiece surfaces of highly complex geometry, such as those associated with gas turbine blades or vanes, are being bonded together. Patents representative of other relevant prior art are U.S. Pat. Nos. 2,424,878 and 2,882,387.